The 300m axles are ideal for high performance engines. They are manufactured in the USA and a far superior product compared to the Chinese made 4130 and 4140 Chromoly axles. 300m axles are aircraft quality CNC machined and race proven. 300m axles are also heat treated after they are machined to ensure strength and durability. Splines are 4 inches long on both ends incase you need to cut them down for your specific application.
How to Measure IRS Axle Length:

1.) First adjust your rear wheel alignment toe in. If your tires are toed out like a duck your trailing arms will be closer to your transmission resulting in a shorter axle.

2.) Lift the trailing arm so that if you did have an axle it would be parallel to the floor at zero degrees. This is your shortest point.

3.) Measure from the center of the drive flange on your transmission to the center of the stub axle on your trailing arm. DONOT measure where your CV joint mounting surface is. You need to measure the bottom of each cup because this is where your axle will plunge into. If you purchase too long of an axle, when your trailing arm moves upward to zero degrees it will shove the axle into the transmission. This will mushroom the ends of your axles and eventually crush the ring gear inside your transmission.

4.) After you have measured this distance, you subtract 1/4 inch total length. For instance if you measure from the center of the drive flange to the center of the stub axle and you get 20 1/2 inches you would buy a 20 1/4 axle.

5.) Measure both sides of the car. It is VERY common to have unequal length axles.